I don't know if Jonas is still there in texas with you but if he is, I have an Idea how to make Bree trait negative.

Since Jules is "Trait Negative", and you know where she lives, maybe you can grab her again and get a sample of her blood.

Then maybe you can get that Spencer guy to analyze some of it, and see if he can figure out what makes it "Trait Nagative". Also you should have some of it handy to inject Bree with, if any of you can get close to enough to her. Maybe Jules blood can make Bree "Trait Negative".

Oh and in case you haven't figured it out yet, Bree's last video had another hidden message: "Friday early low tide yacht club parents slip"_________________Julia, Talyor, Sarah, Bree, will any of you Play with Me?

The major problem with that is mixing blood.
if Jules and Bree are different blood types or types that can't go together Bree's white blood cells would attack the injected Jules blood thinking it is a disease.